import sys
input = sys.stdin.readline

from heapq import heappush, heappop
inf = 10**18
def dijkstra(s, t):
    # ゴールがない場合はg=-1とする。

    N = len(G)

    def cost(v, m):
        return v * N + m

    dist = [inf] * N
    mindist = [inf] * N
    seen = [False] * N
    Edge = [set() for i in range(N)]
    Q = [(cost(0, s), -1)]
    while Q:
        c, p = heappop(Q)
        c, m = divmod(c, N)
        if seen[m]:
            continue
        seen[m] = True
        dist[m] = c
        if t == 0:
            Edge[p].add(m)
            Edge[m].add(p)
        else:
            Edge[p].add(m)

        #------heapをアップデートする。--------
        for u, C in G[m]:
            if seen[u]:
                continue
            newdist = dist[m] + C

            #------------------------------------
            if newdist >= mindist[u]:
                continue
            mindist[u] = newdist
            heappush(Q, (cost(newdist, u), m))
    return dist, Edge

T = int(input())
N, M = map(int, input().split())
G = [[] for i in range(N)]
E = []
if T == 0:
    for i in range(M):
        u, v, c = map(int, input().split())
        u, v = u - 1, v - 1
        G[u].append((v, c))
        G[v].append((u, c))
        E.append((u, v, c))

    ans = inf
    for s in range(N):
        D, Edge = dijkstra(s, T)
        for u, v, c in E:
            if v in Edge[u]:
                continue
            ans = min(ans, D[u] + D[v] + c)
else:
    for i in range(M):
        u, v, c = map(int, input().split())
        u, v = u - 1, v - 1
        G[u].append((v, c))
        E.append((u, v, c))

    ans = inf
    for s in range(N):
        D, Edge = dijkstra(s, T)
        for u, v, c in E:
            if v != s:
                continue
            ans = min(ans, D[u] + c)
        
print(ans) if ans != inf else print(-1)